1. Field of the Invention
The present invention relates to a push switch which prevents an impact noise from being generated during the return of a slider after the slider is pressed.
2. Description of the Related Art
A push switch is publicly known in Japanese Unexamined Utility Model Registration Application Publication No. 5-55420 and shown in FIGS. 9 and 10. In the push switch, an operating member is pressed to bring a movable contact into contact with and separated from a fixed contact, and the movable contact and the fixed contact are accommodated in a casing. If the pressing is released by a return member, these contacts return to their initial positions. Section lines in FIGS. 9 and 10 pass through a front leg and a rear leg which will be described later.
In the drawings, reference numeral 20 denotes a push button switch of a hysteresis mechanism. The push button switch 20 is constructed such that an operating body 22 is mounted on a casing 21, and the operating body 22 is depressed to allow switching operation. The casing 21 of the push button switch 20 is formed with a rectangular bulging portion 23, and the operating body 22 is mounted in the bulging portion 23. That is, sliding portions 24 are suspended from the four corners of the operating body 22, and the sliding portions 24 are formed so as to slide vertically inside the four corners of the casing 21. Therefore, the operating body 22 is mounted to be vertically movable with respect to the casing 21.
A coil spring 25 is fitted into the middle of the rear surface of the operating body 22 and is suspended from the surface. A membrane switch 26 is provided beneath the bottom of the casing 21. A click rubber 27 is provided between the coil spring 25 and the membrane switch 26 such that a head of the click rubber 27 is fitted to a lower portion of the coil spring 25. A pressing portion 28 protruding from the other side of the head of the click rubber 27 is positioned above contacts 29 and 30 of the membrane switch 26.
On the other hand, between a pair of the sliding portions 24 provided back and forth (the front side of the drawing is forth, and the rear side of the drawing is back), a front leg 31 and a rear leg 32 are suspended. Similarly, a front leg 31 and a rear leg 32 are suspended between another pair of sliding portions 24, and lower ends of the front legs 31 project outward to form stoppers 33. Lower ends of the rear legs 32 are provided with projections 34. The projection 34, as shown in FIG. 10, is formed in the shape of a taper which is widened outward from the top toward the bottom. Further, an upper edge 35 of the bulging portion 23 of the casing 23 is stepped. In addition, the stoppers 33 protrude in a direction substantially orthogonal to the legs 31 to be locked to the upper edge 35 of the bulging portion 23.
The projections 34 formed at the rear legs 32, as shown in FIG. 10, are widened from locations slightly above the stoppers 33, and the rear legs 32 are made narrower than the front legs 31. Therefore, the rear legs 32 have a larger elastic force than the front legs 31. That is, the front legs 31 are not bent and the operating body 22 is not separated from the casing 21 unless the operating body 22 is intentionally detached from the casing. On the other hand, the lower edge of the click rubber 27 is provided with an outwardly protruding seat 36. The seat 36 is formed so that the legs 31 can be seated thereon.
When the operating body 22 is pressed, the coil spring 25 urges the click rubber 27 with the decent of the operating body 22, and the pressing portion 28 of the click rubber 27 presses the contact 29 of the membrane switch 26. Accordingly, the contact 29 contacts the contact 30. At this time, the legs 31 are seated on the seat 36 of the click rubber 27, which prevents generation of an impact noise of the legs 31.
When the operating body 22 is released from pressing, the operating body 22 returns to its original uppermost position by an elastic forces of the click rubber 27 and the coil spring 25. At this time, before the stoppers 33 provided at the front legs 31 reach the upper edge 35 of the casing 21, the projections 34 of the rear legs 32 contact the upper edge 35. As the operating body 22 ascends, the legs 32 are bent and pressed against the upper edge 35 of the casing 21.
When the operating body 22 ascends, the stoppers 33 are locked to the upper edge 35 of the casing 21 to stop the ascent of the operating body 22. Accordingly, the pressing of the projections 34 against the upper edge 35 of the casing 21 relieves an impact caused between the stoppers 33 and the casing 21 when the ascent of the operating body 22 stops, which prevents generation of an impact noise.
In such a conventional push switch, before the stoppers 33 of the front legs 31 reach the upper edge 35 of the casing 21, the projections 34 of the rear legs 32 contact the upper edge 35. Also, as the operating body 22 ascends, the legs 32 are bent and pressed against the upper edge 35 of the casing 21. Moreover, when the operating body 22 ascends, the stoppers 33 are locked to the upper edge 35 of the casing 21 to stop the ascent of the operating body 22. Accordingly, the pressing of the projections 34 against the upper edge 35 of the casing 21 relieves the impact caused between the stoppers 33 and the casing 21 when the ascent of the operating body 22 stops, which prevents generation of an impact noise.
However, since the vertical movement of the operating body 22 is guided by the casing 21, the tapered surfaces of the projections 34 of the operating body 22 come into collision with the upper edge 35 of the casing 21, which is not enough to weaken the noise.
Also, the operating body 22 in its non-operative state is positioned by the flat surfaces of the stoppers 33 and the upper edge 35 after the legs 32 are elastically deformed, which requires elasticity to be given to the legs 32. Therefore, the push switch needs to be designed in consideration of the spring pressure of the return members (the click rubber 27 and the coil spring 25), the strength of the legs 32, etc. There are also limitations to the adjustment of the elasticity.
It is an object of the present invention to provide a push switch which prevents generation of an impact noise during the return of an operating body which has been pressed and which has no chattering in a non-operative state.